The increasing difficulties for further scaling down of Si electronics are driving the investigation of alternative channel materials with higher energy efficiency and better performance. Among the large variety of semiconducting materials, single walled carbon nanotubes (SWNTs) are extremely attractive due to their outstanding charge transport properties and ultrathin bodies. One of the most daunting challenge, however, is in creating large-area, perfectly aligned arrays of purely semiconducting SWNTs (s-SWNTs).
Here, we present strategies to address this issue. Nanoscale thermocapillary flows and subsequent etching serve as an effective way to remove the metallic impurities in perfectly aligned arrays of SWNTs grown on quartz substrates. We develop a nanoscale thermometry-scanning Joule expansion microscopy (SJEM) for quantitative assessments of the low temperature nature associated with this process. Measurements combined with simulations fully reveal the essential physics of the thermocapillary flows. We also introduce a simple and scalable scheme to initiate the thermocapillary flows through microwave irradiation of SWNT arrays. Microstrip dipole antennas of low work function metals concentrate the microwaves and selectively couple them into only metallic SWNTs (m-SWNTs). Those efforts allow for complete removal of all m-SWNTs, as revealed through systematic experimental and computational studies. For a demonstration of the effectiveness, we implement this method on large arrays consisting of ~20,000 SWNTs, completely removing all of the m-SWNTs (~7000) to yield a purity of s-SWNTs at a level at least to 99.9925%.
Lastly, we present several demonstrations of electronic and optoelectronic devices based on aligned arrays (both purified and unpurified) and detailed characterization of their performance.